1. Field of the Invention
The present invention relates generally to safety devices for use in connection with fluid pressure systems. More particularly the invention concerns a unique combination fluid pressure gage and safety pressure relief device for automatically venting the fluid pressure system to atmosphere in the event of over-pressurization.
2. Discussion of the Prior Art
Various types of pressure gages have been suggested for use in measuring fluid pressure within pressure systems. Such gages include Bourdon-Tube pressure gages, diaphragm pressure gages, capsule-type pressure gages and piston-type pressure gages. The designers of fluid pressure gages have typically been concerned with gage accuracy, reliability and cost and have left to others the development of hardware adapted to guard against system over-pressurization.
Those concerned with safety devices such as automatic pressure relief devices, on the other hand, have generally not involved themselves with pressure measuring mechanisms. Rather, they have concentrated on the design of various types of self contained mechanisms adapted to be installed as separate units within pressure systems to guard against inadvertant over-pressurization of the system. Typical of prior art pressure relief or safety devices are pop-off valves, burst discs, and various types of in line pressure regulating and pressure limiting devices.
Many prior art pressure relief and safety devices have proven unreliable in use. For example, relief valves of standard design frequently fail to open reliably at their intended pre-set pressure for a variety of reasons. Such devices may fail to open because of improper design, improper maintenance, or accidental or intentional damage to the device. Additionally, prior art devices of ordinary design may fail to open properly because contaminants in the system have succeeded in effectively glueing the relief valve seat to the land surrounding the relief valve bore. This glueing force adds to the force of the relief valve spring and frequently results in the relief valve failing to lift until the pressure within the system has reached a level which may be four or five times the intended pre-set venting pressure.
The apparatus of the present invention for the first time combines into a single, integral unit a highly accurate and reliable pressure gage and a fail safe pressure relief valve mechanism. Due to its unique design, the device of the invention overcomes the drawbacks of prior art devices as previously discussed and prevents the highly dangerous potential failure of the pressure gage itself in the event of system overpressurization.
As will be discussed in greater detail in the paragraphs which follow, the relief mechanism of the apparatus of the invention remains closed so long as the pressure to the gage is within the normal working range at the gage. When the pressure to the gage exceeds the normal full scale pressure, additional travel of the pressure sensing element and associated gage movement will cause venting of an interiorly disposed pilot nozzle, allowing the relief valve to go wide open, thereby venting to atmosphere the excess pressure in the system. Further, because of the unique tripping action design of the relief valve, it will remain wide open until reset by a skilled knowledgeable technician using a special tool. This will normally require that the original cause of system malfunction be corrected before the system can again be pressurized.
Another important aspect of the relief valve of the apparatus of the invention resides in the fact that it will automatically open at a point slightly beyond full scale gage pressure regardless of the nominal range of the gage.